Julius Caesar

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World view

Somewhat like Eratosthenes, the Iranian polymath Al-Biruni (973-1048) was able to estimate the radius of the earth using just a few measurements and some clear thinking. If h is a mountain with a known height and the distance from the mountaintop A to the horizon C can be established accurately, then angle α is the same as angle AOC at the earth’s center and we have everything we need to calculate leg OC of right triangle AOC, which is the radius of the earth.

Biruni carried this out using a tall mountain near Nandana in present-day Pakistan. He estimated the earth’s radius at 6,339.9 km, which is only 16.8 km less than the current value of 6,356.7 km. This accuracy would not be obtained in the West until the 16th century.

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Aanvulling

"Zo rond 1420 had de Iraanse wiskundige al-Kashi \(\pi\) tot op 16 decimalen uitgerekend en de berekening van de sinus van 1 graad door middel van de numerieke oplossing van een derdegraads vergelijking."
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